This application makes reference to, incorporates the same herein, and claims all benefits accruing under 35 U.S.C xc2xa7119 from an application entitled Voice Coding Conversion Circuit Between Office Exchange And ISDN Keyphone System filed in the Korean Industrial Property Office on Dec. 30, 1998 and assigned Serial No. 98-60820.
1. Field of the Invention
The present invention relates generally to a voice coding conversion circuit between an office exchange and an ISDN (Integrated Service Digital Network) keyphone system, and in particular, to a voice coding conversion circuit for converting an xcexc-Law or A-Law voice coding mode of an ISDN keyphone system, supported during basic rate interfacing (BRI), to an A-Law or xcexc-Law (Mu-Law) voice coding mode, respectively, according to a voice coding mode of an office exchange.
2. Description of the Related Art
FIG. 1 shows a block diagram of an ISDN system. Referring to FIG. 1, an ISDN keyphone system 100 is connected to an office exchange 300 via a line termination unit 200. Further, the ISDN keyphone system 100 is connected to a network termination equipment NTE, an intermediate multiplexer IMUX, a primary multiplexer PMUX, and primary network termination equipment PNTE. In the ISDN keyphone system 100 of FIG. 1, a voice coding mode of a BRI card is generally matched to a voice coding mode of the office exchange 300. For example, an office exchange using A-Law voice coding requires an ISDN keyphone system using A-Law voice coding, and an office exchange using xcexc-Law voice coding requires an ISDN keyphone system using xcexc-Law voice coding. Thus it has been necessary to replace the whole ISDN keyphone system using A-Law voice coding with an ISDN keyphone system using xcexc-Law voice coding when an office exchange requires xcexc-Law voice coding, and it has been necessary to replace the whole ISDN keyphone system using xcexc-Law voice coding with an ISDN keyphone system using A-Law voice coding when an office exchange requires A-Law voice coding.
Of interest to the present invention, and incorporated herein, are: U.S. Pat. No. 5,467,395 to Michihiro Izumi and entitled Telephone Exchange Apparatus which discusses an ISDN system utilizing xcexc-Law voice coding; and U.S. Pat. No. 4,747,096 to Joseph Piasecki et al. entitled Combination TASI and ADPCM Apparatus, U.S. Pat. No. 4,403,322 to Takao Kato et al. entitled Voice Signal Converting Device, U.S. Pat. No. 5,060,227 to Roger W. Finley et al. entitled Digital Telephone Switch With Simultaneous Dual PCM Format Compatibility and U.S. Pat. No. 5,239,542 to Charles J. Breidenstein et al. entitled Time Division Multiplex Switching System For Interconnecting Telephone Circuits Which Operate In Accordance With Different Signalling Systems And Call Formats each of which disclose A/xcexc-Law conversion.
It is, therefore, an object of the present invention to provide a circuit for converting a voice coding mode of a BRI card in an ISDN keyphone system according to a voice coding mode of an office exchange.
To achieve the above object, there is provided a circuit for switching PCM voice coding between an ISDN keyphone system and an office exchange. The circuit comprises a controller for generating a control signal for controlling conversion of a voice coding mode of PCM data received s from the ISDN keyphone system to an A-Law voice coding mode or a xcexc-Law voice coding mode according to a coding mode of the office exchange; and an A/xcexc-Law converter for converting the voice coding mode of the PCM data according to the control signal output from the controller so that a voice coding mode of the PCM data output from the ISDN keyphone system matches to a voice coding mode office exchange, and the voice coding mode of the PCM data output by the office exchange matches to a voice coding mode of the ISDN keyphone system. An operator inputs a specific code using a keyboard in an ISDN keyphone system according to a voice coding mode of the office exchange. The controller then provides the A/xcexc-Law converter with a control signal so that a voice coding mode of the PCM data output from the office exchange and input to the ISDN keyphone system is matched to a voice coding mode of the ISDN keyphone system and a voice coding mode of the PCM data output from the ISDN keyphone system and input to the office exchange is matched to a voice coding mode of the office exchange.
Additionally, the controller then provides the A/xcexc-Law converter with a control signal so that a voice coding mode of the PCM data is not converted when the voice coding mode of the ISDN keyphone system and a voice coding mode of the office exchange already match.